"I won't enter it for a week," he answered.  "But you needn't worry about me.  I haven't been experimenting with electricity all this time for nothing, I can tell you.  As for my health, I'm as well and strong as any boy need be, and there's nothing wrong with my head, either. Common folks always think great men are crazy, but Edison and Tesla and I don't pay any attention to that.  We've got our discoveries to look after.  Now, as I said, I'm going for a little trip in the interests of science.  I may be back to-night, or I may be gone several days.  Anyhow, I'll be back in a week, and you mustn't worry about me a single minute."
"How are you going?" inquired his father, in the gentle, soothing tone persons use in addressing maniacs.
"Through the air," said Rob.
His father groaned.
"Where's your balloon?" inquired sister Mabel, sarcastically.
"I don't need a balloon," returned the boy.  "That's a clumsy way of traveling, at best.  I shall go by electric propulsion."
"Good gracious!" cried Mr. Joslyn, and the mother murmured: "My poor boy! my poor boy!"
"As you are my nearest relatives," continued Rob, not noticing these exclamations, "I will allow you to come into the back yard and see me start.  You will then understand something of my electrical powers."
They followed him at once, although with unbelieving faces, and on the way Rob clasped the little machine to his left wrist, so that his coat sleeve nearly hid it.